The present invention relates to a cereal grain color sorting apparatus which optically detects foreign matter mixed in the grains such as rice grains, wheat grains or beans or bad one of the grains mixed therein so as to sort or discriminate and remove the same.
In this specification, "color" of the granular object generally means "the color in visible light region", and the granular object being "transparent" means that, so far as there is no other prescription, "it is transparent to visible light", that is, "it has the property of transmitting therethrough the visible light".
As disclosed in Japanese Patent Unexamined Publication No. 1-258781, for example, in conventional color sorting apparatus, the grain is illuminated with a light source such as incandescent lamp, fluorescent lamp or the like in the visible light region, a difference between an intensity of light from the grain illuminated with the light source and an intensity of light from a background serving as a reference color board is detected by light-receiving elements dedicated to a plurality of wavelength bands in the visible light region respectively, thereby discriminating and removing the foreign matter by making use of a difference in color between good grain and foreign matter. However, in the above-described conventional color sorting apparatus, in the case that the foreign matter such as broken piece of glass, plastics, metal, pottery, china or the like, mixed in the cereal grain had the same color as the good grain or was transparent, appropriate separation and removal of the foreign matter could not be effected.
Japanese Patent Unexamined Publication No. 5-200365 discloses a foreign matter detecting apparatus in which near-infrared light is irradiated to a checking area, and two kinds of light of specific wavelengths (of about 1,300 nm and about 1,460 nm) in the near-infrared region (at wavelengths of 750.about.2,500 nm) are detected out of the light diffused by and transmitted through an object to be checked, and the detected two values are compared with respective predetermined values so as to decide whether the checked object is an desirable object such as white rice grain or a foreign matter such as glass piece or plastic piece, thereby detecting and discriminating from the good grain the foreign matter having the same color as the good grain or being transparent.
However, only with the above-described foreign matter detecting apparatus using the near-infrared light for the light source, bad or undesirable grain and the like cannot be sorted out from the good grain, and therefore, in order to effect discrimination and removal of the bad grain and the like as well, it is necessary to additionally equip the conventional color sorting apparatus using the visible light for the light source. Namely, effective sorting can be performed only in such a manner that ordinary foreign matter having a different color from the good grain is first discriminated and removed from the good grain in the visible light region by the conventional color sorting apparatus and, thereafter, other foreign matter having the same color as the good grain or being transparent is discriminated and removed from the good grain by the foreign matter detecting apparatus using light in the near-infrared light. On the other hand, to incorporate the foreign matter detecting apparatus disclosed in Japanese Patent Unexamined Publication No. 5-200365 in which the near-infrared light is used for the light source, into the conventional color sorting apparatus using light in the visible light region, will cause the apparatus to be too complicated and increased in size as a whole, resulting in that maintenance of the apparatus will be too troublesome.